Top 43 Unrecognized Selector Sent To Instance The 17 Latest Answer

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How do I fix unrecognized selector sent to instance?

The “Unrecognized selector sent to instance” is an annoying error in Xcode.
…
Fixing «Unrecognized Selector Sent To Instance»

First, check that the selector is called on the right object. The function name should exist on that object. …
Then, check the function name. …
Then, check the function parameters.

What does unrecognized selector sent to instance mean?

Once you run this line of code you will instantly get an error message in the console area, which look s like this (unrecognized selector sent to instance). Since the selector is another name for the method, the error is basically saying that it doesn’t recognize the function that you’re trying to call on this object.

What is a selector in Xcode?

A selector is the name used to select a method to execute for an object, or the unique identifier that replaces the name when the source code is compiled. A selector by itself doesn’t do anything. It simply identifies a method.

What is a selector in iOS Swift?

In Objective-C, a selector is a type that refers to the name of an Objective-C method. In Swift, Objective-C selectors are represented by the Selector structure, and you create them using the #selector expression.

What is selector method?

A selector is an identifier which represents the name of a method. It is not related to any specific class or method, and can be used to describe a method of any class, whether it is a class or instance method. Simply, a selector is like a key in a dictionary.

What is a selector in Swift?

Swift version: 5.6. Selectors are effectively the names of methods on an object or struct, and they are used to execute some code at runtime. They were common in Objective-C, but the earliest versions of Swift didn’t include some core selector functionality so their use declined for a while.

What are CSS selectors?

A CSS selector is the first part of a CSS Rule. It is a pattern of elements and other terms that tell the browser which HTML elements should be selected to have the CSS property values inside the rule applied to them.

What are selectors Objective-C?

In Objective-C, selector has two meanings. It can be used to refer simply to the name of a method when it’s used in a source-code message to an object. It also, though, refers to the unique identifier that replaces the name when the source code is compiled.

What is @objc method?

Objective-C is based on a message passing model that is kind like calling methods plus some other goodies. It’s essentially the same as calling a method like in many other programming languages, which is why they are often used interchangeably. Message passing is different in that any message can be sent to any object.

How do I use UITapGestureRecognizer?

The iOS UITapGestureRecognizer class has a built-in way to detect a double tap on any view. All you need to do is create the recognizer, set its numberOfTapsRequired property to 2, then add it to the view you want to monitor.

lesson 13. problem is solved for \” unrecognized selector sent to instance \” Xcode

“unrecognized selector sent to instance” error in Objective-C – Stack Overflow

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Summary of article content: Articles about “unrecognized selector sent to instance” error in Objective-C – Stack Overflow It looks like you’re not memory managing the view controller properly and it is being deallocated at some point – which causes the numberButtonClicked: … …
Most searched keywords: Whether you are looking for “unrecognized selector sent to instance” error in Objective-C – Stack Overflow It looks like you’re not memory managing the view controller properly and it is being deallocated at some point – which causes the numberButtonClicked: …
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Summary of article content: Articles about “Unrecognized selector sent to ins… | Apple Developer Forums I am trying to create a DropDownMenu , but when I try to call addTarget to a UIButton this error comes up… ‘unrecognized selector sent to instance … …
Most searched keywords: Whether you are looking for “Unrecognized selector sent to ins… | Apple Developer Forums I am trying to create a DropDownMenu , but when I try to call addTarget to a UIButton this error comes up… ‘unrecognized selector sent to instance …
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Understanding Selectors in Swift and Objective-C

Using Selectors in Swift 22 to 50

Fixing «Unrecognized Selector Sent To Instance»

“unrecognized selector sent to instance” error in Objective-C

In my case the function was not expecting an argument but the button was configured to send one causing the error. To fix this I had to rewire the event handler.

Here is my function:

Notice it contains no arguments.

Here is an image of my button configuration (right click on the button to view it):

Notice there are 3 event handlers.

To fix this I had to remove each of the event items since one of them was sending a reference to itself to the enterPressed function. To remove these items I clicked on the little x icon next to the name of each item until there were no items shown.

Next I had to reconnect the button to the event. To do this hold down the Control key and then drag a line from the button to the action. It should say “Connect Action”. Note: I had to restart XCode for this to work for some reason; otherwise it only let me insert actions (aka create a new action) above or below the function.

You should now have a single event handler wired to the button event that passes no arguments:

This answer compliments the answer by @Leonard Challis which you should read as well.

“Unrecognized selector sent to ins…

The #selector(DropDownMenu.onclick) vs #selector(DropDownMenu.onclick(_:)) makes no difference.

#selector(DropDownMenu.onclick)

#selector(DropDownMenu.onclick(_:))

onclick(???)

The error gets called when I click on the button, not when I call addTarget.

The function never gets called though.

addTarget(target, #selector(…), …)

target

target

andare exactly the same thing unless you have anothermethod.Thanks for clarifying. That helps me solve your issue. But not enough.Please be more specific. What is the function?I guess the function is a method of your ViewController which is not shown yet.Have forgotten again? As I said, you should better show the whole code of your view controller .If you write, the instance held inneeds to respond to the selector.In your code,is an instance of your ViewController.Does your ViewController really respond to all the selectors you have written?Does your ViewController reallyto respond to all the selectors you have written?Anyway, you may need to clarify which method of which class you expect to be called on which event.

Unrecognized Selector Sent to Instance – AppyPie

Fixing The «Unrecognized Selector Sent to Instance» Error in Xcode

Aasif Khan | December 9, 2021 4:41 pm | 4-min read By

The “Unrecognized selector sent to instance” is an annoying error in Xcode. With Swift’s syntax improvements this error occurs less often, but it still pops up every now and then. How do you solve it?

In this tutorial, you’ll learn to debug Unrecognized selector sent to instance. We’ll discuss where the error comes from and how to solve it.

Debugging is part of becoming an effective iOS developer. Fixing errors is a great way to learn more about iOS development, so take your time to go in-depth.

Understanding Selectors in Swift and Objective-C

Selectors are a relic from the past, from Objective-C. With the latest Swift, you shouldn’t run into that Unrecognized selector sent to instance problem that often.

But… what’s a selector?

A selector is essentially the name of a function. You “select” which function to execute on an object based on the selector. You can safely assume that a selector is identical to the name of a function.

Selectors come from Objective-C:

SEL or Selector is the variable type of a selector

In Objective-C, you could create a selector with the @selector() function or with NSSelectorFromString(@”methodName”)

In Objective-C, you could execute a selector on an object with the performSelector: function, and test whether an selector exists with respondsToSelector:

In Swift, we use #selector() to indicate a function to be called, with the target-action mechanism

So why does this Unrecognized selector sent to instance error then show up in Swift code?

A large part of the Cocoa Touch SDK, i.e. the framework code you use to create native iOS apps, is still written in Objective-C! Especially the UIKit framework, the one that puts views, images and buttons on your iPhone screen, is written in Objective-C.

Many Objective-C classes use the target-action mechanism. It’s a special way of calling functions. Check this out:

let gesture = UITapGestureRecognizer(target: self, action: #selector(onTapGesture(_:)))

gesture.numberOfTapsRequired = 1

view.addGestureRecognizer(gesture)

@objc func onTapGesture(_ gesture:UITapGestureRecognizer)

{

print(“Tapped!!”)

}

In the above example, you’re creating a gesture recognizer that executes the onTapGesture(_:) function when you tap the screen once. This code can be part of a UIViewController, for instance.

Do you see the target and action parameters in the UITapGestureRecognizer initializer function?

With the target-action design pattern you’re essentially saying: “When this happens, execute that function.”

The target is the object the function is called upon, and the action is the function that should be called. In many cases you can also designate an event with the for parameter, for instance to execute the action when the value on a textfield changes.

Now you know where selectors come from!

Using Selectors in Swift 2.2 to 5.0

Selectors have been part of the Swift programming language since it was invented, because selectors originally come from Objective-C. Because the iOS SDK is partly written in Objective-C, you still work with selectors in Swift.

Before Swift 2.2 you used Objective-C selectors like this:

let gesture = UITapGestureRecognizer(target: self, action: Selector(“onTapGesture:”))

See how the Selector initializer takes one argument, a string, that contains the name of the function that should be called? Now you’re starting to see where this might go wrong…

The string with the selector can’t be checked at runtime! The Swift compiler can’t check whether the function actually exists before you run your app, so if you’ve written the selector incorrectly, you’ll get that Unrecognized selector sent to instance.

If Swift could have checked whether the selector exists when compiling the app, it would have shown you the Use of unresolved identifier error.

On top of that, the syntax for writing out selectors is confusing. Ever noticed those colons, parentheses and underscores?

When a function has no parameters, you write onTapGesture()

When a function has one unnamed parameter, you write onTapGesture(_:)

When a function has multiple unnamed parameters, you write onTapGesture(_:_:), i.e. one _: for every unnamed parameter

When a function has one named parameter, you write the name of the parameter like this onTapGesture(gesture:)

When a function has multiple named parameters, you write the names of the parameters, like this onTapGesture(gesture:view:event:)

Objective-C doesn’t have parentheses for function names, because of its bracket-style messaging syntax, so you wouldn’t write them in the selector string: onTapGesture:.

Quick Tip: If you want to know the selector or function name of the current function, use print(#function) in Swift.

So… here’s the kicker: since Swift version 2.2, selectors can be checked at during compilation thanks to a new syntax:

let gesture = UITapGestureRecognizer(target: self, action: #selector(onTapGesture(_:)))

Instead of using a string, the new #selector() syntax refers directly to the function that should be called when the event takes place.

Because of this, Swift can pre-check during compilation whether a function exists, and inform you of an error before you run your app. The result? Less time debugging your app!

In Swift 4 and later you’ll have to designate functions that you want to use as selectors for target/action-based interactions with @objc. This is because Swift 4 doesn’t automatically make Swift functions available to Objective-C.

The quirky way of writing functions with underscores and colons remains, however. Fortunately, you can use code autocompletion to get hints, like this:

Simply place your cursor between the parentheses of #selector() and press the Esc-key. A dropdown menu shows up, and you can scroll to the right function.

Still got the error? Let’s get to fixing it…

Fixing «Unrecognized Selector Sent To Instance»

Alright, enough with the explaining! You now know where the Unrecognized selector sent to instance comes from and what causes it – so let’s get to fixing.

If you’re coding Objective-C, or working with Swift 1.0, 2.0 or 2.1. (i.e. before Swift 2.2), this solution is for you.

With Swift 2.2, the error shouldn’t happen, because it’s checked at compile-time. If you still run into issues with a selector, check this tutorial and use code completion to get to the right selector.

First off, let’s be real:

If you’re a beginner coder, switch to learning Swift. It’s much easier than Objective-C, it’s widely adopted, and it’s the designated programming language for the future of iOS.

If you’re still on a Swift version before 5.0, make sure to upgrade! Sure, it’s a bit of work, but Swift 5.0 has a better, more productive syntax and is much more stable than previous Swift versions.

If you’re debugging an Objective-C library, or you can’t upgrade to the latest Swift version, do this:

First, check that the selector is called on the right object. The function name should exist on that object. You’d typically check the target argument for the target-action design pattern. In many cases, the target should be self. Then, check the function name. Make sure it uses the exact uppercase and lowercase letters – the selector must be identical to the function in order to work. Then, check the function parameters. They must be identical too! This is where those quirky colons and underscores come in, so you’ll need to use the right format. You can use print(#function) (Swift >= 2.2), or print(__FUNCTION__) (Swift < 2.2), or NSLog(@"%s", __PRETTY_FUNCTION__) in Objective-C to find out the correct selector. In some cases, Xcode won’t take you to the offending line after a crash. When your app crashes you won’t see the line of code that caused the crash, but instead you’ll be taken to your AppDelegate class. How do you find the incorrect line of code now? If you look at the entire error output, you’ll see that it has caused an exception: *** Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[MyApp.MyViewController viewDidLoad:]: unrecognized selector sent to instance 0xDEADBEEF’ You can catch that exception with a clever trick: First, open the Breakpoint Navigator on the left of Xcode Then, click on the +-button in the bottom-right corner Then, choose Exception Breakpoint Finally, a new breakpoint should show up in the navigator Run your app and trigger the error. You should now see the line that is incorrect, because thanks to the breakpoint your code “breaks” on the line of code that threw the exception. In rare cases, especially if you haven’t managed memory correctly, you can get the Unrecognized selector sent to instance error on an object that shouldn’t have received that selector in the first place. This can happen when you incorrectly retain and/or release objects, causing an object to be allocated on a memory address that was previously associated with another object. Because this new object doesn’t have the selector you’re trying to call, you’ll see the error. You can solve this by tracing the memory leak. Further Reading Alright! Solved the error? Awesome! Now you know what selectors are, how to use them, and why they can cause all sorts of problems… Create Your App Now

So you have finished reading the unrecognized selector sent to instance topic article, if you find this article useful, please share it. Thank you very much. See more: NSInvalidArgumentException, Unrecognized selector sent to instance Swift, NSInvalidArgumentException Swift, 0x8000000000000000, Terminating with uncaught exception of type NSException, Terminating app due to uncaught exception ‘NSInvalidArgumentException, UITapGestureRecognizer, Add tap gesture recognizer to UIView Swift

Top 43 Unrecognized Selector Sent To Instance The 17 Latest Answer

How do I fix unrecognized selector sent to instance?

What does unrecognized selector sent to instance mean?

What is a selector in Xcode?

What is a selector in iOS Swift?

What is selector method?

What is a selector in Swift?

What are CSS selectors?

What are selectors Objective-C?

What is @objc method?

How do I use UITapGestureRecognizer?

“unrecognized selector sent to instance” error in Objective-C – Stack Overflow

“Unrecognized selector sent to ins… | Apple Developer Forums

Unrecognized Selector Sent to Instance – AppyPie

Fixing “Unrecognized Selector Sent To Instance” Error In Xcode

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Fixing “Unrecognized Selector Sent To Instance” Error In Xcode

Unrecognized Selector Sent to Instance – AppyPie

Unrecognized Selector Sent to Instance – Using Swift – Swift Forums

Unrecognized Selector Sent to Instance – Using Swift – Swift Forums

Unrecognized selector sent to instance – iOS – raywenderlich.com Forums

iOS 14 unrecognized selector sent to instance exception on IoTHubClient_LL_DoWork() · Issue #1624 · Azure/azure-iot-sdk-c · GitHub

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